Polymers for control of orientation and stability of liquid crystals

ABSTRACT

An electro-optically active polymer gel material comprising a high molecular weight alignment polymer adapted to be homogeneously dispersed throughout a liquid crystal to control the alignment of the liquid crystal molecules and/or confer mechanical stability is provided. The electro-optically active polymer gel comprises a homogenous gel in which the polymer strands of the gel are provided in low concentration and are well solvated by the small molecule liquid crystal without producing unacceptable slowing of its electrooptic response. During formation of the gel, a desired orientation is locked into the gel by physical or chemical cross-linking of the polymer chains. The electro-optically active polymer is then utilized to direct the orientation in the liquid crystal gel in the “field off” state of a liquid crystal display. The electro-optically active polymer also provides a memory of the mesostructural arrangement of the liquid crystal and acts to suppress the formation of large scale deviations, such as, for example, fan-type defects in a FLC when subjected to a mechanical shock. A method of making an electro-optically active polymer gel material and an electrooptic device utilizing the electro-optically active polymer gel of the present invention is also provided.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is based on U.S. application Ser. No.60/194,990, filed Apr. 5, 2000, the disclosure of which is incorporatedby reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] The U.S. Government has certain rights in this invention pursuantto grant No. F49620-97-1-0014, awarded by the Air Force Office ofStrategic Research, Liquid Crystals M.U.R.I.

FIELD OF THE INVENTION

[0003] This invention relates generally to alignment materials for usein liquid-crystal electrooptic devices. More specifically, thisinvention relates to polymeric alignment materials that reduce oreliminate the need for separate polymeric alignment layers and provideimproved mechanical stabilization to liquid crystals.

BACKGROUND OF THE INVENTION

[0004] Liquid crystal electrooptic devices such as flat panel displaysrely on active alignment, or control, of the orientation of the liquidcrystal molecules when no field is applied. A parameter of a liquidcrystal structure, such as director orientation or smectic layerstructure, may be said to be actively aligned if alignment layers inducea preferred configuration on the parameter and if when the preferredconfiguration is perturbed, the alignment layers exert a restoring forceor torque.

[0005] There are a number of different conventional methods forcontrolling the orientation of the liquid crystals in the absence of afield. For example, in a twisted nemantic display, the liquid crystalorientation is anchored at the surfaces on each side of the device andaligned parallel to the surfaces using rubbed polymer layers where therubbing directions are mutually orthogonal to produce a twisted liquidcrystal configuration. There are a number of difficulties associatedwith this approach, mainly associated with the rubbing procedure that isneeded to induce the orientation in the alignment layers.

[0006] More problematic are smectic liquid crystal displays, such as,for example, ferroelectric liquid crystals (FLCs), used for bi-stabledisplays or newer analog “thresholdless FLC” devices. For FLC displaypanels and other smectic LCDs, the structure of the smectic layers aswell as the orientation of the director is an important parameter. Forexisting smectic LCDs, the smectic layers of the FLC must be aligned ina “bookshelf arrangement,” and this orientation of the FLC is producedusing polymer alignment layers with special thermal histories.

[0007] In addition to the same problems caused by rubbing that occur innematic displays, a major deficiency in this means of controlling theoriented state is that they are very susceptible to mechanicaldisruption and alignment generally does not recover after having beenperturbed by mechanical stress. However, for LCDs containing the moreordered smectic liquid crystal materials, the smectic layer structure isonly passively aligned by cooling through the nematic to smectic phasetransition, i.e., there is no uniquely specified periodicity in theinteraction between the alignment layer and adjacent liquid crystalmolecules defining the alignment which the smectic layers should adopt.Thus, if this alignment is disturbed in the smectic phase, there is noforce acting to restore the original alignment. Accordingly, a smallmechanical shock can disrupt the orientation state, causingorientational defects to form, which cannot be removed by any existingtechnology. So while smectic LCDs and, in particular, ferroelectric LCDsare strong contenders for use in high definition television (HDTV)displays, memory displays, and computer work stations, their poorresistance to mechanical shock currently limits commercial FLC devicesto small sizes, typically less than a few centimeters on a side. Thereare known ways of reducing this problem, such as, for example, throughthe use of damped mountings and adhesive spacer techniques forfabrication of FLC panels. However, these techniques are not effectiveagainst all possible types of mechanical damage, such as a sudden impactor continuous pressure.

[0008] Several patents attempt to address the problems associated withthe stability of conventional liquid crystal displays via variousconventional mechanical alignment layer means. For example, JP 52 411discloses an arrangement in which dichromatic molecules are bonded to analignment layer. Liquid crystal molecules then align on the layer ofdichromatic molecules. However, this method still has the problem of aweak alignment layer-liquid crystal layer interface. Meanwhile, EP 307959, EP 604 921 and EP 451 820 all disclose various techniques forobtaining particular structures within ferroelectric liquid crystallayers which are intended to provide improved mechanical stability.However, the structures disclosed in the specifications are incompatiblewith high speed, high contrast addressing schemes and are therefore ofvery limited application. EP 635 749 discloses an adhesive spacertechnique for the fabrication of FLC display panels so as to providemore resistance to mechanical damage. However, as describedhereinbefore, techniques of this type are not effective against allpossible types of mechanical damage. Also, EP 467 456 discloses the useof a liquid crystal gel layer as an alignment layer. However, this typeof alignment layer is used merely to control the pre-tilt angle of theliquid crystal material in the cell and does not improve the mechanicalstability.

[0009] A second method for aligning liquid crystals uses aphase-separated polymer to control alignment and provide mechanicalstability, rather than an alignment layer. There are two generaltechniques, polymer-dispersed liquid crystals and polymer-stabilizedliquid crystals. These systems function similar to alignment layers, inthat the interactions between the liquid crystal molecules and thepolymer occur only at the interface between the solid polymer and theliquid crystal. Typically, the polymer is synthesized in situ byphotochemistry or thermally triggered crosslinking of monomer (ormacromer) dissolved into the liquid crystal. As the molecular weight ofthe polymer grows, the system phase-separates into polymer rich, solidand liquid crystal rich, nematic or smectic phases. The nature of theliquid crystal orientation at the resulting liquid crystal polymerinterfaces is typically controlled by the structure of the polymer orsurface-active agents that are incorporated in the system. In somecases, the orientation direction is influenced using an applied electricor magnetic field during polymerization so that the resulting polymerprovides a lasting memory of the orientation state. In this techniquethe alignment polymer is made anisotropic by applying a flow or anelectric field, then after the desired orientation of the solvatedmonomer or prepolymer is generated, the polymer is transformed so thatit provides a lasting memory of the orientation state, e.g., byphotochemically or thermally-triggered cross-linking. These techniquesdo improve the mechanical stability of the liquid crystals.

[0010] For example, GB 2 274 652 discloses an arrangement in which aconventional low molar mass ferroelectric liquid crystal mixture isdoped with a polymeric additive. However, while this arrangement isintended to improve mechanical stability, of ferroelectric liquidcrystals it results in reduced switching speed for the electroopticdevice.

[0011] Similarly, EP 586 014 discloses arrangements of a polymer networkcreated by photoinitiated polymerization of an aligned liquid crystalcontaining monomer. However, while this arrangement does improvemechanical stability, it results in reduced switching speed for theelectrooptic device.

[0012] Finally, S. H. Jin et al, “Alignment of FerroelectricLiquid-crystal Molecules by Liquid-Crystalline Polymer,” SID 95 Digest,(1995) 536-539 discloses the use of a main chain thermotropic liquidcrystal polymer as an alignment layer for an FLC cell. However, theliquid crystal alignment is obtained by conventional mechanical rubbingof this layer, the liquid crystal polymer being in its glassy phase atroom temperature.

[0013] Accordingly, a need exists for an improved material for use inaligning liquid crystal electrooptic devices which reduces or eliminatesthe need for a separate alignment layer and which provides greatermechanical stabilization to a wide range of fast switching liquidcrystal displays.

SUMMARY OF THE INVENTION

[0014] The present invention is directed to an electro-optically activepolymer gel material comprising an alignment polymer adapted to behomogeneously dispersed throughout a liquid crystal to control thealignment of the liquid crystal molecules and confer mechanicalstability. This invention utilizes a homogenous gel in which the polymerstrands of the gel are provided in low concentration such that they arewell solvated by the small molecule liquid crystal. A desiredorientation is then locked into the gel by physical or chemicalcross-linking of the polymer chains. The orientation of the polymers, isthen utilized to direct the orientation field in the liquid crystal inthe “field off” state of a liquid crystal display. In this invention thestrands of the polymer also provide a memory of the mesostructuralarrangement of the liquid crystal and act to suppress the formation oflarge scale deviations, such as, for example, fan-type defects in an FLCwhen subjected to a mechanical shock.

[0015] In one embodiment, the invention is directed to anelectro-optically active, homogeneously dispersed polymer gel layer ofliquid crystalline material comprising a permanently orientedanisotropic network of polymerized material containing molecules of atleast one sparsely cross-linked homogeneously dispersed polymer solvatedby molecules of at least one liquid crystalline material or mesogen,wherein the polymer is provided in low enough concentrations such thatthe switching response of the liquid crystal polymer gel is acceptablyfast for electrooptic operations. In one particular embodiment thepolymer is adapted to mechanically stabilize the gel. Any suitablepolymer and liquid crystal mixture can be utilized such that the polymeris fully solvated by the liquid crystal molecules, such as, for example,a side-chain or main-chain polymer block or telechelic polymer having aliquid crystal mesogen. Any suitable method of forming theelectro-optically active polymer gel layer may be utilized, such as, forexample, by self-assembly of a main-chain or side-chain block copolymer,by photopolymerization of a soluble macromer, or by a mixture of thetwo.

[0016] Although any suitably dilute concentration of polymer may beutilized such that the switching speed of the liquid crystal is notsignificantly reduced (for example, where the switching time more thandoubles over the switching time of the pure liquid crystal molecules)and such that the polymer molecules are capable of sparselycross-linking to form the polymer network, in one preferred embodimentthe electro-optically active layer comprises less than 5% of the gellayer by mass and more preferably equal to or less than 2% of the gellayer by mass.

[0017] Likewise, although any high molecular weight polymer may beutilized such that the polymer is capable of sparsely cross-linking evenat dilute concentrations, in a preferred embodiment the polymer has amolecular weight of at least 100,000 g/mol, more preferably at least500,000 g/mol, and even more preferably at least 1 million g/mol.

[0018] In another embodiment, the homogeneously dispersed polymercomponent of the electro-optically active polymer gel is selected suchthat the polymer molecules dictate the alignment of the liquid crystalmolecules in the absence of an electric field. In this embodiment anyalignment geometry suitable for the desired liquid crystal material orelectrooptic device may be induced in the gel, such as, for example,uniaxial, twisted, supertwisted, tilted, or bookshelf.

[0019] In yet another embodiment, the liquid crystal molecules areselected from the group of fluorinated or cyanobiphenyl (CB) basedliquid crystal molecules.

[0020] In still another embodiment, the network of liquid crystalmolecules comprises a plurality of self-assembly block copolymers eachcomprising at least one endblock and at least one midblock, wherein theendblock either physically or chemically cross-links with at least oneother endblock and wherein the midblock is soluble in the liquid crystalmolecules. In such an embodiment the endblock may be insoluble in theliquid crystal molecules thereby physically aggregating to form thepolymer network. In such an embodiment the midblock may further comprisea plurality of liquid crystal side-chains, wherein the liquid crystalside-chains confer solubility to the block copolymer in the liquidcrystal molecules, or alternatively the midblock may be a main-chainpolymer comprising a plurality of liquid crystal mesogens, and whereinthe main-chain confers solubility to the block copolymer in the liquidcrystal molecules, or in yet another alternative the midblock maycomprise a mixed side-chain/main-chain polymer, where at least one ofthe main-chain or the side-chain confers solubility to the blockcopolymer in the liquid crystal molecules.

[0021] In such an embodiment the cross-linking may occur at any point onthe polymer chain. For example, the polymer molecules may becross-linked only at the ends or the midblock may further comprise atleast one linking block, wherein the linking block is either physicallyor chemically cross-links with either the linking block or endblock ofanother polymer.

[0022] In still yet another such embodiment the endblock may be madecrosslinkable with other endblocks by application of either a photo orthermal initiating energy. In such an embodiment the photo initiatingenergy may be any suitable energy, such as, for example, UV-light,X-ray, gamma-ray, and radiation with high-energy electrons or ions.

[0023] In still yet another embodiment, the network of liquid crystalmolecules comprises a plurality of self-assembly telechelic polymerseach comprising at least one crosslinking functional group, where thecrosslinking functional group either physically or chemicallycross-links with at least one other crosslinking functional group andwherein the telechelic polymer is soluble in the liquid crystalmolecules. In such an embodiment, the crosslinking functional group maybe insoluble in the liquid crystal molecules. Also in such an embodimentthe telechelic polymer may further comprise a plurality of liquidcrystal side-chains, where the liquid crystal side-chains confersolubility to the telechelic polymer in the liquid crystal molecules, oralternatively the telechelic polymer may be a main-chain polymercomprising a plurality of liquid crystal mesogens, where the main-chainconfers solubility to the telechelic polymer in the liquid crystalmolecules, or again alternatively the telechelic polymer may comprise amixed side-chain/main-chain polymer, where at least one of themain-chair or the side-chain confers solubility to the telechelicpolymer in the liquid crystal molecules.

[0024] In such an embodiment the telechelic polymer may be cross-linkedby any suitable means. For example, the telechelic polymer may furthercomprise at least two crosslinking groups at either end of thetelechelic polymer.

[0025] In an alternative embodiment the crosslinking group is madecrosslinkable with other crosslinking groups by application of either aphoto or thermal initiating energy. In such an embodiment the photoinitiating energy may be selected from any suitable source, such as, forexample, UV-light, X-ray, gamma-ray, and radiation with high-energyelectrons or ions.

[0026] In still yet another alternative embodiment, the liquid crystalmolecules are aligned according to a geometry selected from the groupconsisting of: uniaxial, twisted, supertwisted, tilted, chevron andbookshelf.

[0027] In still another embodiment, the invention is directed to anelectrooptic device incorporating the electro-optically active gel layerof the invention. Any suitable electrooptic device may be utilized, suchas, for example, a liquid crystal display device or anelectroluminescent lamp.

[0028] In still yet another embodiment, the invention is directed to amethod for constructing an electrooptic device utilizing theelectro-optically active gel layer of the invention. The methodcomprising homogeneously dispersing a small quantity of the highmolecular weight polymer described above into a quantity of liquidcrystal molecules, orienting the liquid crystal molecules and polymersand sparsely crosslinking the polymers to form an anisotropic polymernetwork adapted to mechanically stabilize the liquid crystal molecules.In such a method the anisotropic polymer network may also be adapted todictate the alignment of the liquid crystal molecules.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] These and other features and advantages of the present inventionwill be better understood by reference to the following detaileddescription when considered in conjunction with the accompanyingdrawings wherein:

[0030]FIG. 1a is a schematic view of a system for aligning liquidcrystal molecules according to the prior art.

[0031]FIG. 1b is a schematic view of a system for aligning liquidcrystal molecules according to the prior art.

[0032]FIG. 1c is a schematic view of a system for aligning liquidcrystal molecules according to the prior art.

[0033]FIG. 1d is a schematic view of a system for aligning liquidcrystal molecules according to the present invention.

[0034]FIG. 2a is a schematic view of a polymer liquid crystal alignmentsystem according to the present invention.

[0035]FIG. 2b is a schematic view of a polymer liquid crystal alignmentsystem according to the present invention.

[0036]FIG. 2c is a schematic view of a polymer liquid crystal alignmentsystem according to the present invention.

[0037]FIG. 3 is a synthesis pathway of an embodiment of the polymeraccording to the present invention.

[0038]FIG. 4 is a synthesis pathway of an embodiment of the polymeraccording to the present invention.

[0039]FIG. 5 is a synthesis pathway of an embodiment of the polymeraccording to the present invention.

[0040]FIG. 6 is a graphical representation of the liquid crystalproperties of a liquid crystal system according to the presentinvention.

[0041]FIG. 7 is a graphical representation of the liquid crystalproperties of a liquid crystal system according to the presentinvention.

[0042]FIG. 8 is a graphical representation of the liquid crystalproperties of a liquid crystal system according to the presentinvention.

[0043]FIG. 9 is a schematic diagram of an electrooptical deviceincorporating the electroelectro-optically active liquid crystalmaterial of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0044] The present invention is directed to an electro-optically activeliquid crystal gel comprising a low concentration sparsely cross-linkedhomogeneously dispersed liquid crystal soluble polymer and a mixture ofliquid crystal molecules.

[0045] As discussed above, there are a number of different methods forcontrolling the orientation of the liquid crystals. FIGS. 1a to 1 cschematically show the conventional methods for inducing alignmentcontrol in liquid crystal electrooptical devices. FIG. 1a shows theconventional rubbed polymer method of orienting both nemantic andferroelectric displays 10. In this method, the liquid crystal molecules12 are disposed between surfaces 14 on each side of the device 10 andaligned parallel to the surfaces 14 using rubbed polymer layers 16.There are a number of difficulties associated with this approach, mainlyassociated with the rubbing procedure that is needed to induce theorientation in the alignment layers 16. In addition, mechanical stresscan cause disruption of the liquid crystal structure and in somedisplays, such as, for example, ferroelectric display's alignment doesnot always recover after having been perturbed by mechanical stress.

[0046] A second general method for aligning liquid crystals 12 is shownin FIGS. 1b and 1 c and uses polymer molecules 18 to control alignmentand provide mechanical stability, rather than a separate mechanicalalignment layer. There are two general techniques, polymer-stabilizedliquid crystals, shown in FIG. 1b, and polymer-dispersed liquidcrystals, shown in FIG. 1c. In contrast to the use of alignment layers,in which the interactions between the liquid crystal molecules 12 andthe polymer 18 occur only at the interface 16 between the solid polymerlayer and the liquid crystal 12, the polymer-dispersed andpolymer-stabilized techniques provide intimate contact between thepolymer molecules 18 and the liquid crystal 12. In this technique, thealignment polymer 18 is typically made anisotropic by either analignment layer or by applying an electric field, then after the desiredorientation of the solvated polymer 18 is generated, the polymer 18 istransformed so that it provides a lasting memory of the orientationstate, e.g., by photochemically or thermally-triggered polymerization ofmesomers or cross linking of oligomers or thermally triggered physicalassociation. Although these techniques do improve the mechanicalstability of the liquid crystals 12, the current techniques rely on highconcentrations of polymer 18 to achieve cross-linking which cansignificantly slow down switching times and efficiency. In addition,polymer-dispersed liquid crystals can sometimes require high appliedswitching voltages and display devices made using both of thesetechniques tend to be hazy.

[0047] The electro-optically active gel layer 20 in accordance with thepresent invention is shown in FIG. 1d. The electro-optically active gellayer 20 comprises a dilute solution of an anisotropic network 23 ofpolymer 24 solute homogeneously dispersed within a solvent comprising ahomogeneous or heterogeneous mixture of small liquid crystal molecules22. The anisotropic network 23 of cross-linkable polymer 24 soluteitself comprises a cross-linkable backbone 26 and a plurality of liquidcrystal mesogens 28 attached thereto. The anisotropic network of polymer24 is characterized in that an orientation can be induced into thepolymer 24 via an external orienting influence and then frozen into ananisotropic network 23 of polymer molecules 24 via a physical orchemical cross-linking reaction between the individual polymers 24. Theunbound ferroelectric or nematic liquid crystal molecules 22 of theelectro-optically active material 20 in solution with the polymer 24solute are then subject to interactions with the oriented anisotropicnetwork 23 of polymer 24 such that the orientation of the liquid crystalmolecules 22 is dictated by the orientation of the anisotropic networkof polymer 24.

[0048] Any homogenous or heterogenous mixture of liquid crystalmolecules 22 can be utilized as a solvent such that theelectro-optically active layer 20 is in a gel state and exhibitsnematic, chiral nematic, ferroelectric, antiferroelectric orelectroclinic properties and such that during operation the liquidcrystal molecules 22 exhibit a suitable electro-optically active phaseunder conventional operating conditions for an electrooptic device, suchas, for example, a nematic, chiral nematic, smectic C chiral smectic Cor smectic A phase at temperatures in the range from about −10° to 60°C. Because a variety of different electrooptic devices are contemplated,any suitable liquid crystal molecules or mixtures can be used, such as,for example, nemalic cyanobiphenyl (CB) based liquid crystals oreutectic mixtures thereof, or ferroelectric phenylbenzoate (PB) basedliquid crystals, Zli 3654 (Merck) or eutectic mixtures thereof orvarious fluorinated liquid crystals or eutectic liquid crystal mixtures.In another embodiment, liquid crystal molecules 22 having dichroicproperties are utilized such that a polarizer is not required in anyelectrooptical device utilizing the electro-optically active material 20of the invention.

[0049] The polymer 24 solute is chosen such that it is soluble in theliquid crystal molecules 22 solvent and can be sparsely cross-linkedeven under dilute conditions to form an oriented anisotropicthree-dimensional polymer network 23 which is a liquid crystal gelelectro-optically active material 20. Although any suitably diluteconcentration of polymer 24 may be utilized such that the switchingspeed of the liquid crystal is not significantly reduced (for example,where the switching time more than doubles over the switching time ofthe pure liquid crystal molecules 22) and such that the polymermolecules 24 are capable of sparsely cross-linking to form the polymernetwork, in one preferred embodiment the electro-optically active layercomprises less than 5% of the gel layer by mass and more preferablyequal to or less than 2% of the gel layer by mass.

[0050] In light of the functional requirements, high molecular weightpolymer molecules 24, such as, for example, polymers with a molecularweight of at least 100,000 g/mol, more preferably at least 500,000g/mol, and even more preferably polymers with a molecular weight of atleast 1 million g/mol, having side-unit or main-chain liquid crystalgroups or mesogens 28 with an affinity for the liquid crystal molecules22 of the electro-optically active material 20 and having only a fewinsoluble and/or cross-linking blocks or functional groups 30 arechosen. Within the structural features listed above, however, anypolymer 24 that can coordinate or bond with the chosen liquid crystaland which provides sufficient field-off anisotropy and/or suitablestructural stability can be utilized in the current invention, such as,for example, block or telechelic polymers. Furthermore, the polymer 24can be made using any suitable technique, such as, for example, radical,anionic, or polymer analogous, in which the polymer backbone 26 is firstmade, then a mesogen 28 added, and then the polymers are cross-linkedvia a cross-linkable end portion 30. The liquid crystal mesogen 28 canbe linked to the polymer via any suitable means, such as, for example,by incorporation of the mesogen 28 into the main-chain of the polymer orattachment of the mesogen 28 as a side-unit, with or without a spacer31. Likewise, although only end cross-linking or insoluble groups 30 areshown, it should be understood that such groups 30 may be positioned atany point along the chain of the polymer 24.

[0051]FIGS. 2a to 2 c schematically depict three possible polymers 24according to the present invention. FIG. 2a depicts the reaction betweena polymer backbone 26 and a liquid crystal mesogen 28 in which theliquid crystal 28 is attached as a side-unit to the backbone 26 to forma side-chain polymer 24 according to the present invention. FIG. 2bshows the reaction between a plurality of liquid crystal mesogens 28 into form EL main-chain polymer 24 according to the present invention.Finally, FIG. 2c depicts the formation of a block or telechelic polymerhaving end-units 30 attached to either end of the backbone 26 to providea crosslinking function to the polymer 24 according to the presentinvention.

[0052] Although the embodiments of the polymer 24 shown in FIGS. 2a to 2c all depict either main-chain or side-chain block polymers, it shouldbe understood that any polymer 24 with the suitable alignment,structural and solubility characteristics could be utilized in theelectro-optically active gel layer 20 according to the presentinvention. In addition, any suitable method of cross-linking theindividual polymer molecules 24 to form the polymer network 23 of theelectrooptically active material 20 can be utilized. For example, in theembodiment of the invention shown in FIG. 2c, the anisotropic network 23is created by self-assembly of a block copolymer 24 comprising endblocks 30 that are insoluble in the liquid crystal molecules 22 suchthat they aggregate to form the physical cross-links and midblocks orbackbones 26 that are soluble in the liquid crystal molecules 22. Inanother embodiment, the polymer network 23 of the current invention isformed by photo or thermally polymerizing the end blocks 30 of aprepolymer or macromer 24 that is soluble in the desired liquid crystalmolecules 22. Any suitable photo or thermal polymerizable end block 30may be used, such as, for example, acrylates, methacrylates, epoxycompounds and/or thiolene systems. In the case of photo-polymerization,an additional photo-initiator may be required, such as, for example,Igacure 651 (Merck). Any suitable radiation may be used to trigger thephotopolymerization, such as, for example, UV-light, X-rays, gamma-raysor radiation with high-energy particles such as electrons and ions

[0053] In either such embodiment the solubility of the midblock orbackbone 26 of the polymer 24 is conferred either by soluble unitswithin the main-chain (as shown schematically in FIG. 2b), byside-groups selected to confer solubility (as shown in FIG. 2a), or by amixture of the two techniques. Any suitable solubilizing units ormesogens 28 can be utilized, such as, for example, any homogenous orheterogenous mixture of liquid crystal molecules exhibiting nematic,ferroelectric, antiferroelectric or electroclinic properties and suchthat the mesogens 28 have an affinity for the liquid crystal molecules22 of the electro-optically active material 20. Such mesogens 28 mayexhibit any suitable electro-optically active phase, such as, forexample, a nematic, chiral nematic, chiral smectic C, smectic C orsmectic A phase. Because a variety of different electrooptic devices arecontemplated, any suitable liquid crystal molecules or mixtures can beused, such as, for example, nematic cyanobiphenyl (CB) based liquidcrystals or eutectic mixtures thereof, or ferroelectric phenylbenzoate(PB) based liquid crystals, Zli 3654 (Merck) or eutectic mixturesthereof, or of various fluorinated liquid crystals or eutectic mixturesthereof. In another embodiment, mesogens 28 having dichroic propertiesare utilized such that a polarizer is not required in any electroopticaldevice utilizing the electro-optically active material 20 of theinvention.

[0054] Orientation can be induced in the liquid crystal molecules 22 byany suitable technique. For example, uniaxial, twisted, supertwisted,tilted, chevron and bookshelf orientations of the liquid crystalmolecules 22 can be induced in the electro-optically active material 20of the current invention by varying the orientation directions oforientation layers and the thickness of the cell holding theelectro-optically active material 20 as shown in FIG. 1a and then fixingthe orientation by cross-linking the polymers 24 of theelectro-optically active material 20 to form an oriented polymer network23 as described above. Although orientation layers do provide one methodof providing an initial orientation to the electro-optically activematerial 20 of the current invention, it should be understood thatorientation layers are not needed to maintain orientation of the liquidcrystal molecules 22, as in many conventional electro-optically activematerials, since such orientation is provided by the polymer network 23itself In one embodiment, then, a desired orientation is first providedby an external field or flow, such as, for example, an electrical ormagnetic field, or an oscillatory or unidirectional shear induced flow,or an extensional stress and then the induced orientation is fixed viacross-linking of the polymer molecules 24 and formation of theanisotropic polymer network 23.

[0055] The invention is also directed to a method of forming theelectro-optically active liquid crystal gel according to the invention.Accordingly, in one exemplary embodiment, an electro-optically activematerial 20 of the current invention was formed utilizing a polymeranalogous approach. The electro-optically active gel solution 20 wasformed by mixing cyanobiphenyl liquid crystal molecules 22, with acyanobiphenyl polymer 24 synthesized according to the reaction scheme inFIG. 3. The cyanobiphenyl or C13 based liquid crystal molecules 22 canbe synthesized according to conventional techniques or alternativelypurchased either as a purified substance, such as, for example, CB5 orCB50 (Merck) or as a mixture of liquid crystal molecules, such as, forexample E7 or E44 (Merck). In this mixture the backbone 26 of thepolymer 24 is a 1,2-polybutadiene polymer 24, synthesized according tothe reaction scheme in FIG. 4. Alternatively, the polymer may besynthesized according to the reaction scheme shown in FIG. 5. Toencourage crosslinking of the polymer molecules, conventional end blocksor end functional groups 30 are added to the mixture. These groups mayprovide either physical or chemical cross-linking under a variety ofconditions. To prevent aggregation, or cross-linking before anorientation has been induced in the gel, the mixture is brought to ahigh temperature at which aggregation does not occur. Although thistemperature may vary according to the cross-linking group utilized,typically a temperature of about 80° C. ensures that the polymermolecules can still flow. At this temperature the mixture is usually inthe nematic phase, and can be oriented under the influence of aconventional alignment layer, an external electric field, or a shearstrain. Under said conditions an anisotropic orientation of theelectro-optically active material 20 is obtained. Subsequently, thepolymer 24 is made to cross-link or aggregate to form an anisotropicnetwork and an electro-optically active layer either by simply coolingtemperature of mixture to a point at which self-assembly of thecross-linkable units 30 aggregate or cross-link, typically about 30° C.,or via photo or thermal initiate cross-linking. Although the abovemethod utilizes a polymer analogous approach to synthesize the polymer24 according to the invention, it should be understood that any suitablemethod may be used, such as, for example, by radical or aniontechniques. Likewise, although a block copolymer is described anysuitable polymer may be synthesized, such as, for example a telechelicpolymer.

[0056] Because dilute solutions of high molecular weight polymers havenever been used to make electro-optically active materials, FIGS. 6 to 8show a series of experiments taken using solutions of the high molecularweight polymers according to the invention. FIG. 6 shows that theaddition of a low concentration of a high molecular weight polymeraccording to the present invention can yield high rheological control ofliquid crystal alignment. In this case a solution of only 10% polymerhaving a molecular weight of 800,000 g/mol in a solution of liquidcrystal molecules causes the liquid crystal molecules to becomeflow-aligning not merely parallel to the velocity direction as insolutions containing similar concentrations of small molecular weightpolymers, but to become flow-aligning parallel to the velocity gradientdirection. Such flow-aligning characteristics indicate that lowconcentrations of the high molecular weight polymers of the currentinvention can yield electro-optically active materials having excellentrheological control properties previously only obtainable using highconcentrations of low molecular weight polymers.

[0057]FIG. 7 shows that the polymer solutions according to the inventioncan be obtained with a variety of pure liquid crystals and liquidcrystal mixtures, such as, for example 50 CB and 5 CB (Merck) as well asin several eutectic mixtures of liquid crystal molecules, such as, forexample E7 and E44 (Merck). While these cyanobiphenyl and eutecticmixtures have been utilized in the current embodiments, it should beunderstood that such optical properties can also be obtained with avariety of other liquid crystal molecules and eutectic mixtures thereof.

[0058] The electro-optically active gel material 20 of the currentinvention is characterized in that the solution of liquid crystalmolecules 22 solvent to polymer 24 solute is a dilute solution such thatthe switching speed of the electrooptically active material 20 remainsfast. FIG. 8 shows a graph of switching time verse the percent polymer24, as described above having a molecular weight of ˜800,000 g/mol, inthe liquid crystal solution. Typical electrooptical devices, such as,for example, liquid crystal display devices have switching times ofabout 10 ms. Typically, polymer aligning agents are only useful if theswitching time of the liquid crystal with the aligning agent is lessthan double the switching time of the pure liquid crystal material. Asshown in FIG. 8, the pure liquid crystal material used in the embodimentshown has a switching time of ˜14.6 ms/μm² and any increase in thequantity of the polymer 24 leads to a substantial increase in theswitching time of the device. In the present case, then, the quantity ofpolymer 24 is held at about 2% or less, as calculated by weight percentof the polymer to solution such that the switching time of theelectrooptical device remains less than double the pure liquid crystalswitching time. However, this concentration is measured for nematicdisplays, which are significantly slower than ferroelectric displays. Assuch, it should be understood that the concentration of polymer inferroelectric displays could be significantly increased given theinherent switching time of such devices. For example, in the presentcase, concentrations as high as 6% could be used.

[0059]FIG. 9 diagrammatically shows a cross-sectional view of anelectrooptic device capable of utilizing the electro-optically activematerial in accordance with the invention, when configured as a displaydevice 32. The display device 32 comprises two glass substrates 34 and36 which are provided with a matrix of transparent electrode layers 38and 40 on the sides facing each other. The electrode layers 38 and 40can be individually drive via electrically conductive tracks (notshown). On the matrix of the electrode layers 38 and 40 there areprovided an orientation layer 42 and 44 of rubbed polyimide. Thedistance 46 between both orientation layers 42 and 44 forms thethickness of the electro-optically active layer 48 described above. Byorienting and then fixing the electro-optically active layer 48 asdescribed above, an oriented electro-optically active layer 48 can beobtained. Although a passive matrix display 32 is described herein, itshould be understood that any electrooptic device could be manufacturedutilizing the electro-optically active material of the presentinvention, such as, for example, an active matrix display.

[0060] The elements of the apparatus and the general features of thecomponents are shown and described in relatively simplified andgenerally symbolic manner. Appropriate structural details and parametersfor actual operation are available and known to those skilled in the artwith respect to the conventional aspects of the process.

[0061] Although specific embodiments are disclosed herein, it isexpected that persons skilled in the art can and will design alternativeelectro-optically active materials and electrooptic devices that arewithin the scope of the following claims either literally or under theDoctrine of Equivalents.

What is claimed is:
 1. An electro-optically active gel layer havingnematic, ferroelectric, antiferroelectric or electroclinic propertiescomprising a quantity of aligned liquid crystal molecules having ananisotropic three-dimensional polymer network homogeneously dispersedtherein, wherein the polymer network comprises a plurality of sparsleycross-linked polymer molecules.
 2. An electro-optically active gel layeras described in claim 1, wherein the polymer network dictates thealignment of the molecules.
 3. An electro-optically active gel layer asdescribed in claim 1, wherein the polymer comprises less than 5% of thegel layer by mass.
 4. An electro-optically active gel layer as describedin claim 1, wherein the polymer comprises equal to or less than 2% ofthe gel layer by mass.
 5. An electro-optically active gel layer asdescribed in claim 1, wherein the polymer has a molecular weight of atleast 1 million g/mol.
 6. An electro-optically active gel layer asdescribed in claim 1, wherein the polymer is a fluorinated polymer. 7.An electro-optically active gel layer as described in claim 1, whereinthe electro-optically active material has a switching time less thandouble the switching time of the liquid crystal molecules in the absenceof the polymer.
 8. An electro-optically active gel layer as described inclaim 1, wherein the polymer is either a block copolymer or telechelicpolymer.
 9. An electro-optically active gel layer as described in claim1, wherein the polymer molecules are cross-linked only at the ends. 10.An electro-optically active gel layer as described in claim 1, whereinthe homogeneously dispersed polymer network of liquid crystal moleculescomprises a plurality of self-assembly block copolymers each comprisingat least one endblock and at least one midblock, wherein the endblockeither physically or chemically cross-links with at least one otherendblock and wherein the midblock is soluble in the liquid crystalmolecules.
 11. An electro-optically active gel layer as described inclaim 10, wherein the endblock is insoluble in the liquid crystalmolecules.
 12. An electro-optically active gel layer as described inclaim 10, wherein the midblock further comprises a plurality of liquidcrystal side-chains, wherein the liquid crystal side-chains confersolubility to the block copolymer in the liquid crystal molecules. 13.An electro-optically active gel layer as described in claim 10, whereinthe midblock is a main-chain liquid crystal polymer comprising aplurality of liquid crystal mesogens, and wherein the main-chain conferssolubility to the midblock of the polymer in the liquid crystalmolecules.
 14. An electro-optically active gel layer as described inclaim 10, wherein the midblock comprises a mixed side-chain/main-chainliquid crystal polymer, and wherein at least one of the main-chain orthe side-chain structures confers solubility to the midblock of polymerin the liquid crystal molecules.
 15. An electro-optically active gellayer as described in claim 10, wherein the endblock further comprisesat least one linking block, wherein the linking block either physicallyor chemically cross-links with either the linking block or endblock ofanother polymer.
 16. An electro-optically active gel layer as describedin claim 10, wherein the endblock is made crosslinkable with otherendblocks by application of either a photo or thermal initiating energy.17. An electro-optically active gel layer as described in claim 16,wherein the photo initiating energy is selected from the groupconsisting of: UV-light, X-ray, gamma-ray, and radiation withhigh-energy electrons or ions.
 18. An electro-optically active gel layeras described in claim 1, wherein the network of liquid crystal moleculescomprises a plurality of self-assembly telechelic polymers eachcomprising at least one crosslinking functional group, wherein thecrosslinking functional group either physically or chemicallycross-links with at least one other crosslinking functional group andwherein the telechelic polymer is soluble in the liquid crystalmolecules.
 19. An electro-optically active gel layer as described inclaim 18, wherein the crosslinking functional group is insoluble in theliquid crystal molecules.
 20. An electro-optically active gel layer asdescribed in claim 18, wherein the telechelic polymer further comprisesa plurality of liquid crystal side-chains, wherein the liquid crystalside-chains confer solubility to the telechelic polymer in the liquidcrystal molecules.
 21. An electro-optically active gel layer asdescribed in claim 18, wherein the telechelic polymer is a main-chainpolymer comprising a plurality of liquid crystal mesogens, and whereinthe main-chain confers solubility to the telechelic polymer in theliquid crystal molecules.
 22. An electro-optically active gel layer asdescribed in claim 18, wherein the telechelic polymer comprises a mixedside-chain/main-chain polymer, and wherein at least one of themain-chain or the side-chain confers solubility to the telechelicpolymer in the liquid crystal molecules.
 23. An electro-optically activegel layer as described in claim 18, wherein the telechelic polymerfurther comprises at least two crosslinking groups at either end of thetelechelic polymer.
 24. An electro-optically active gel layer asdescribed in claim 18, wherein the crosslinking group is madecrosslinkable with other crosslinking groups by application of either aphoto or thermal initiating energy.
 25. An electro-optically active gellayer as described in claim 24, wherein the photo initiating energy isselected from the group consisting of: UV-light, X-ray, gamma-ray, andradiation with high-energy electrons or ions.
 26. An electro-opticallyactive gel layer as described in claim 1 wherein the liquid crystalmolecules are aligned according to a geometry selected from the groupconsisting of: uniaxial, twisted, supertwisted, tilted, chevron andbookshelf.
 27. An electro-optically active gel layer having nematic,ferroelectric, antiferroelectric or electroclinic properties comprisinga quantity of liquid crystal molecules having an anisotropicthree-dimensional polymer network homogeneously dispersed therein,wherein the polymer network comprises a plurality of sparselycross-linked polymer molecules, wherein the liquid crystal moleculescomprises less than 5% of the gel layer by mass.
 28. Anelectro-optically active gel layer as described in claim 27, wherein thepolymer network further dictates the alignment of the liquid crystalmolecules.
 29. A method of manufacturing an electro-optically active gellayer comprising: providing a quantity of liquid crystal molecules;providing a quantity of polymer; homogeneously dispersing the quantityof polymer into the quantity of liquid crystal molecules; orienting theliquid crystal molecules and polymers; and sparsely crosslinking thepolymers to form an anisotropic polymer network.
 30. A method ofmanufacturing an electro-optically active gel layer as described inclaim 29, wherein the anisotropic polymer network is also adapted todictate the alignment of the liquid crystal molecules.
 31. A method ofmanufacturing an electro-optically active gel layer as described inclaim 29, wherein the polymer is either a block copolymer or atelechelic polymer.
 32. A method of manufacturing an electro-opticallyactive gel layer as described in claim 29, wherein the polymer is madeusing a technique selected from the group consisting of: anionic,radical and polymer analogous.
 33. A method of manufacturing anelectro-optically active gel layer as described in claim 29, wherein theliquid crystal molecules are oriented by a method selected from thegroup consisting of: surface alignment, energetic field alignment, shearstress alignment, and extensional stress alignment.
 34. A method ofmanufacturing an electro-optically active gel layer as described inclaim 29, wherein the polymers are aligned according to a geometryselected from the group consisting of: uniaxial, twisted, supertwisted,tilted, chevron and bookshelf.
 35. A method of manufacturing anelectro-optically active gel layer as described in claim 29, wherein thepolymer comprises less than 5% of the gel by mass.
 36. A method ofmanufacturing an electro-optically active gel layer as described inclaim 29, wherein the polymer comprises equal to or less than 2% of thegel by mass.
 37. A method of manufacturing an electro-optically activegel layer as described in claim 29, wherein the polymer is eitherchemically or physically crosslinked.
 38. A method of manufacturing anelectro-optically active gel layer as described in claim 29, wherein thepolymer is crosslinked by self-assembly.
 39. A method of manufacturingan electro-optically active gel layer as described in claim 29, whereinthe polymer is crosslinked by thermal or photo initiation.
 40. A methodof manufacturing an electro-optically active gel layer as described inclaim 39, wherein the photo initiation uses an energy selected from thegroup consisting of: UV-light, X-ray, gamma-ray, and radiation withhigh-energy electrons or ions.
 41. A method of manufacturing anelectro-optically active gel layer as described in claim 29, wherein thepolymer is crosslinked by a combination of self-assembly and thermal orphoto initiation.
 42. A method of manufacturing an electro-opticallyactive gel layer as described in claim 29, wherein the polymer has amolecular weight of at least 1 million g/mol.
 43. An electrooptic devicecomprising two substrates, which are provided with at least oneelectrode, and an electro-optically active gel layer which is locatedbetween the two substrates, wherein the electro-optically active gellayer has nematic, ferroelectric, antiferroelectric or electroclinicproperties and comprises a quantity of aligned liquid crystal moleculeshaving an anisotropic three-dimensional polymer network homogeneouslydispersed therein, wherein the polymer network comprises a plurality ofsparsely cross-linked polymer molecules.
 44. An electrooptic device asdescribed in claim 43, wherein the polymer network further dictates thealignment of the liquid crystal molecules.
 45. An electrooptic device asdescribed in claim 43, in the form of a display device.
 46. Anelectrooptic device comprising two substrates, which are provided withat least one electrode, and an electro-optically active gel layer whichis located between the two substrates, wherein the electro-opticallyactive gel layer has nematic, ferroelectric, antiferroelectric orelectroclinic properties and comprises a quantity of aligned liquidcrystal molecules having an anisotropic three-dimensional polymernetwork homogeneously dispersed therein, wherein the polymer networkcomprises a plurality of sparsely cross-linked polymer molecules,wherein the liquid crystal molecules comprises less than 5% of the gellayer by mass, and wherein the polymer network mechanically stabilizesthe liquid crystal molecules.
 47. An electrooptic device as described inclaim 46, wherein the polymer network further dictates the alignment ofthe chiral liquid crystal molecules.
 48. An electrooptic device asdescribed in claim 46, in the form of a display device.
 49. Anelectro-optically active gel layer as described in claim 1, wherein thepolymer network mechanically stabilizes the liquid crystal molecules.50. An electro-optically active gel layer as described in claim 27,wherein the polymer network mechanically stabilizes the liquid crystalmolecules.
 51. A method for manufacturing an electro-optically activegel layer as described in claim 29, wherein the polymer networkmechanically stabilizes the liquid crystal molecules.
 52. Anelectro-optic device as described in claim 43, wherein the polymernetwork mechanically stabilizes the liquid crystal molecules.
 53. Anelectro-optically active gel layer as described in claim 1, wherein thepolymer has a molecular weight of at least 100,000 g/mol.
 54. Anelectro-optically active gel layer as described in claim 29, wherein thepolymer has a molecular weight of at least 100,000 g/mol.
 55. Anelectro-optically active gel layer as described in claim 43, wherein thepolymer has a molecular weight of at least 100,000 g/mol.